Technical Field
The present disclosure relates to a lock-up device, and particularly to a lock-up device for a torque converter, which is configured to transmit a torque from a front cover to a transmission-side member through a turbine.
Background Information
Torque converters are often equipped with a lock-up device for directly transmitting a torque from a front cover to a turbine. Such a lock-up device includes a piston, an input-side plate, a plurality of torsion springs, and an output-side plate. The piston is capable of being coupled by friction to the front cover. The input-side plate is fixed to the piston. The torsion springs are supported by the input-side plate. The output-side plate is elastically coupled through the torsion springs to the piston and the input-side plate in a rotational direction. The output-side plate is fixed to the turbine.
Additionally, as described in Japan Laid-open Patent Application Publication No. 2013-217452, a type of lock-up device has been also proposed in which a plurality of friction facings are used to increase its clutch capacity.
In the lock-up device described in Japan Laid-open Patent Application Publication No. 2013-217452, a clutch plate is disposed between the front cover and the turbine. A lock-up state (power transmission state) is herein made when the clutch plate is contacted to the front cover and the piston while being pressed therebetween. In this state, a torque from the front cover is directly transmitted to the turbine without through a torque converter body.
In the lock-up device described in Japan Laid-open Patent Application Publication No. 2013-217452, an oil chamber plate is disposed between the piston and the turbine, and an oil chamber for activating the piston is defined between the piston and the oil chamber plate. The inner peripheral end of the oil chamber plate is fixed by welding to the outer peripheral surface of a sleeve-shaped boss fixed to the front cover.
In this construction, when hydraulic oil is supplied to the oil chamber, a force acts on the oil chamber plate in a direction separating from the piston. When the oil chamber plate is deformed by the force, chances are that the aforementioned space defined between the piston and the oil chamber plate does not function as the oil chamber. Additionally, deformation of the oil chamber plate bears a risk of damage or breakage thereof. Therefore, the oil chamber plate is required to have a large thickness to enhance its stiffness.